HONE YOUR PROBLEM-SOLVING SKILLS
Twenty tadpoles of a certain frog species, 15 adult snails (collected from ponds containing deformed frogs), and identical amounts of phytoplankton (small algae that grow suspended in water) and attached algae (that grow on rocks) were added to each of ten freshwater tanks.
Atrazine (an herbicide that is often found in ponds) was added to five of these tanks; no atrazine was added to the other five tanks. After 6 months, the mean values shown in the table were determined for phytoplankton abundance, attached algae abundance, water clarity (measured on a scale of 1-5, where 1 is most cloudy and 5 is mostly clear), number of tadpole eosinophils (a type of white blood cell used in the tadpole's immune response), tadpole survival, and number of cysts of the trematode parasite Ribeiroia.| Treatment | ||
| Variable | Atrazine added | No atrazine |
| Phytoplankton (abundance index) | 2.1 | 6.4 |
| Attached algae (abundance index) | 1.4 | 0.9 |
| Water clarity (scale 1-5) | 4.9 | 3.8 |
| Eosinophils (number/ml blood) | 1.2 | 2.7 |
| Tadpole survival (%) | 45.0 | 72.0 |
| Ribeiroia cysts (number/tadpole) | 28.6 | 6.9 |
1. Identify the control used in this experiment. How would investigators use the controls to help them interpret experimental results?
2. Describe the results for phytoplankton abundance, attached algae abundance, and water clarity. Interpret these results.
3. Describe the results for eosinophil number, tadpole survival, and number of Ribeiroia cysts. Interpret these results.
4. Based on the results in the table and the Ribeiroia life cycle (see Figure 1.3), describe a chain of events that could affect a frog population after atrazine was added to a pond.
LIST OF KEY TERMS
abiotic adaptation biosphere biotic climate change community consumer controlled experiment ecology ecosystem environmental science hypotheses landscapes natural selection net primary production (NPP) nutrient cycle population producer
Replication
scale
scientific method